The invention relates to partially hydrophobic silicas, a process for their preparation, their use as carrier for hydrolysis-sensitive active substances and their use in defoaming agents.
The use of hydrophobic silicas in a hydrophobic liquid for the preparation of a defoaming agent is known (DE-C 2829906); U.S. Pat. No. 4,377,493; DE-C 3411 759; U.S. Pat. No. 4,344,858; Kalman Koczo et al., Journal of Colloid and Interface Science 166, 225-238 (1994), WO 95/05880).
Known defoaming agents consist of a mixture of non-polar oils and hydrophobic particles. The solids content is typically 1-20%. These mixtures are more effective defoaming agents than the oil or the hydrophobic particles alone. Defoaming agents are used in the textile, paper, paint, coating and detergent industries.
Known crop protection agents are substantially used in the form of wettable powders, as dust concentrates, dispersible granulates or as emulsifiable concentrates.
Known wettable powders (WP) consist of the following components:
Pesticide active substance, carrier, dispersing and wetting agents as well as optionally additional additives. Thorough premixing of these constituents is followed by coarse milling succeeded by fine milling. Use is in the form of an aqueous spray.
Known dust concentrates consist solely of active substance and filler. Formulations by analogy with the formulation of wettable powders. Fine milling is, however, often omitted.
The dust is applied as dust (DP) after blending with mineral fillers such as kaolin, talcum or dolomite.
Known dispersible granulates (WG) are solid formulations consisting of pesticide active substance, carrier, dispersing and wetting agent as well as optionally other additives. This mixture is finely milled and then granulated using known methods. Use takes the form of aqueous sprays.
Known emulsifiable concentrates (EC) are liquid and contain solvent-containing constituents. Attempts are made to replace the emulsifiable concentrates by solid formulations to avoid solvents that can pose a burden to the environment.
The use of hydrophilic precipitated silica as carrier in the preparation of crop protection agents, pest control agents or concentrated cattle feedstuffs is known (DE-B 16 19 865). The silicas conventionally used have a high oil uptake and a high absorption capacity.
The reduced storage stability of the active substances is, however, a disadvantage in the use of the known precipitated hydrophilic silicas in the preparation of agents containing active substances that are sensitive to hydrolysis. This applies in particular to active substances used in crop protection which could hitherto only be further processed as emulsifiable concentrates because of their sensitivity to hydrolysis.
Known hydrophobic precipitated silicas, such as the precipitated silicas according to DE 26 28975 C2, DE-C 27 29 244, DE-A 24 35 860, EP-A 492 124, and DE-A 25 13 608, are fully hydrophobized and therefore have the disadvantage of needing a large amount of wetting agent in the formulation.
It is therefore an object to provide a carrier for, in particular, hydrolysis-sensitive active substances, such as crop protection agents or feedstuffs as well as active substances from the chemical industry which ensures a longer storage stability of the active substance.
When defoaming agents are used, the known silica has the disadvantage that this silica sediments out when the defoaming agent is stored for longer periods, in particular with the use of low-viscous oils and a low solids content. The defoaming activity deteriorates because of sedimentation of the known silica. Moreover, the sedimented silica also has to be stirred up again in a laborious process before the defoaming agent is used. To prevent a tendency to sedimentation, it may be necessary to add a dispersing agent to the defoaming mixture, such as for example a pyrogenic silica, as well as the known silica (Degussa Technical Bulletin Pigments No. 42, page 11). This necessitates a change in the defoaming formulation which, in turn, necessitates further testing, makes the product more expensive and means an additional process step to work in the dispersing agent.
It is, for example, known from DE 28 29 906 C3 that the defoaming active substances may be prepared in such a manner as to achieve a high dispersion stability by adding to a mixture of a defoaming oil and an emulsifier first the hydrophobic and then the requisite amount of hydrophilic silica, with further stirring.
The instant invention has an advantage over this preparation in that the silica can be stirred into a defoaming oil in one process step and then dispersed, thereby obtaining a stable defoaming dispersion without an additional process step.